Abstract

In a series of experiments, the masking of AM by FM and the masking of FM by AM was investigated. All modulation was sinusoidal, and the carrier was a 1 kHz tone. The masking of 16‐Hz AM by FM as a function of the modulation frequency of the FM showed the same broad tuning seen with AM modulation masking [Bacon and Grantham, 2575–2580 (1989)]. This is consistent with FM being primarily encoded as AM for small modulation depths. Masking of 16‐Hz FM by AM showed broader tuning; this can be attributed to the ‘‘second cue’’ for FM hypothesized by Edwards and Viemeister [ 733–740 (1994)]. AM detection thresholds also were obtained as a function of the modulation index, β, of the FM masker. Thresholds approached 100% modulation depth for large β, indicating an inability to process energy fluctuations that occur in both time and frequency. Finally, thresholds were obtained as a function of the relative phase between the masker and signal modulations. These phase results are discussed with respect to current modulation encoding theories. [Work supported by DC00683.]